Is there any golden rules for this, or am I going to have to guess? I've been doing 30-60s depending on the tea, but some teas need more time after I resteeped a few times. I just received quite a few whites and oolongs that I want to resteep a lot. I also like blacks (two or three times with 60s+), greens (varies) including sencha, and rooibos. I've been using 4.5g tea (2 cups) at a time lately if that matters.

4.5 grams per 2 cups? As in 16 ounces? Just trying to understand what you are doing currently. If this is the case, adding more leaf will likely improve your results.

You kinda nailed it, resteeping times will vary greatly, but another variable is temp.

For most greens, I tend to increase time and temp with each subsequent steeping. The first resteep usually includes a shorter steep than the first at maybe slightly higher temp. Then each resteep I increase time and temp. This could apply for whites as well.

Thing is, there is no one correct way as it becomes a subjective issue based upon personal taste ... and other factors such as your water. Basic guidelines will take you so far, then you need to find your groove.

There are no rules, because it varies by the tea, the quantity of leaf, the temp of the water, and your preferences. But a rule of thumb that I use is to give the tea more time for the first infusion, when it's mostly absorbing water and not yet yielding much, than the second, when it's already wet and ready to release faster, and increase the time the third infusion back close to the first. After that, the increase is determined by the flavor of the previous--too weak? longer. Too strong? shorter. Just right? a little longer. And if it's a cool brewed tea, the water temp gets hotter as I go along too.

So here's a sequence for a japanese sencha I drank recently: 150 degrees, 20 seconds (too short)155°30"165°45"160°90"170°120"and the next time I did 60", 45", 60", 90", 120" with better results.

How much do you change the temperature and only for greens and whites? I'm just trying gauge how much. I'm guessing 5-10F. My kettle does six preset temperatures with differences ranging 5-15F, and these cover almost all recommended temperatures for a variety of teas. I'm usually within 5F of the recommendation. It's a hassle waiting for the water to cool and measuring the temperature, and results are usually satisfactory anyway.

I only change temperatures for those teas that are started with cooler water--with hot-brewed teas (and for me that's gradually progressed to essentially all oolongs and most puerhs as well as black teas), the water starts out at the highest setting on my kettle--205°and stays there. How much and how fast to progress--that's up to your taste buds. Play with it and see. When the infusion you're drinking seems bland, and sweet/floral/herbaceous highlights seem to be gone, and the tea is more grassy than delightful, that's when I start heating it up more.